MOSCOW (AP) _ Three workers at the Chernobyl nuclear power plant dove voluntarily into a pool of radiation-contaminated water under the reactor to drain the water and prevent a steam explosion, Tass reported Thursday.

The official Soviet news agency said the initial fire and explosion at the plant on April 26 wrecked its water-cooling system.

Tass said that 10 days after the explosion, water had collected in a pool under the reactor. If the white-hot core of the reactor had dropped into the water, it could have set off a series of steam explosions that would have spread radioactive contamination farther than the initial disaster.

Three men in wetsuits dived into a pool, probing with underwater searchlights for two small valves that would allow the pool to drain.

Tass said one of the men, Alexei Ananenko, told Soviet journalists, ″When the searchlight beam fell on a pipe, we were joyous: The pipe led to the valves.

″We heard the rush of water out of the tank. And in a few more minutes we were being embraced by the guys,″ Tass quoted Ananenko as saying.

Ananenko was asked by his boss to go into the contaminated water, but also was told he could refuse the hazardous assignment.

″But how could I do that when I was the only person on the shift who knew where the valves were located,″ Tass quoted him as saying.

Physicist Yevgeny Velikhov, vice president of the Soviet Academy of Sciences and one of the directors of the Chernobyl cleanup, said last week that the worst was over after the water was drained from the pool.

Tass identified the other two men as V. Bespalov, a senior engineer, and B. Baranov, shift supervisor at the power station.

″Everyone at the Chernobyl NPS (nuclear power station) was watching this operation,″ Ananenko, a senior engineer-mechanic, was quoted as saying.

After their dive was successful, he said the workers looked at the huge, modern reactor and marveled at its complex systems.